Files lost in backup process

I have an old iMac running 10.4. Pre intel model.
While backing up to external drive I accidentally did the opposite and inadvertently erased half my files. I've found software that may recover files but not for the non intel macs and the OS I'm using. I'm really hoping you can help as these were vital files. Thank you!

Supports down to 10.3.9
You won't want to install it on the drive you're going to try and recover - so you'll need to boot in by FireWire on a back up OS and install it on that. Or on another machine.
cheers